J : 1，2，3，4，5，6，7，8，9， ......
B: 1，2，-2，3，4，-4，5，6，-6， ......
Rearrange the elements in B with the above method, and then naturally get a J->; One-to-one mapping of B. But the expression of F is not easy to find, so we change the order of elements in B so that all odd numbers are positive integers and all even numbers are their own negative even numbers, so we only need to establish one-to-one mapping of odd numbers and positive integers. That is:
J : 1，2，3，4，5，6，7，8，9， ......
B: 1，-2，2，-4，3，-6，4，-8，5， ......
1. When x=2n- 1, f(x)=(x+ 1)/2.
2. When x=2n, f (x) =-x.
It should be noted that here n is also a positive integer starting from 1, but the independent variable of the mapping f is x, not n!